Using CMake with GNU Make: How can I see the exact commands?

I use CMake with GNU Make and would like to see all commands exactly (for example how the compiler is executed, all the flags etc.).

GNU make has --debug, but it does not seem to be that helpful are t开发者_C百科here any other options? Does CMake provide additional flags in the generated Makefile for debugging purpose?

When you run make, add VERBOSE=1 to see the full command output. For example:

cmake .
make VERBOSE=1

Or you can add -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON to the cmake command for permanent verbose command output from the generated Makefiles.

cmake -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON .
make

To reduce some possibly less-interesting output you might like to use the following options. The option CMAKE_RULE_MESSAGES=OFF removes lines like [ 33%] Building C object..., while --no-print-directory tells make to not print out the current directory filtering out lines like make[1]: Entering directory and make[1]: Leaving directory.

cmake -DCMAKE_RULE_MESSAGES:BOOL=OFF -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON .
make --no-print-directory

It is convenient to set the option in the CMakeLists.txt file as:

set(CMAKE_VERBOSE_MAKEFILE ON)

Or simply export VERBOSE environment variable on the shell like this: export VERBOSE=1

If you use the CMake GUI then swap to the advanced view and then the option is called CMAKE_VERBOSE_MAKEFILE.

cmake --build . --verbose

On Linux and with Makefile generation, this is likely just calling make VERBOSE=1 under the hood, but cmake --build can be more portable for your build system, e.g. working across OSes or if you decide to do e.g. Ninja builds later on:

mkdir build
cd build
cmake ..
cmake --build . --verbose

Its documentation also suggests that it is equivalent to VERBOSE=1:

--verbose, -v

Enable verbose output - if supported - including the build commands to be executed.

This option can be omitted if VERBOSE environment variable or CMAKE_VERBOSE_MAKEFILE cached variable is set.

Tested on Cmake 3.22.1, Ubuntu 22.04.

I was trying something similar to ensure the -ggdb flag was present.

Call make in a clean directory and grep the flag you are looking for. Looking for debug rather than ggdb I would just write.

make VERBOSE=1 | grep debug

The -ggdb flag was obscure enough that only the compile commands popped up.

CMake 3.14+

CMake now has --verbose to specify verbose build output. This works regardless of your generator.

cd project
cmake -B build/
cmake --build build --verbose

It's worth noting however Xcode may not work with --verbose

Some generators such as Xcode don't support this option currently.

Another option it to use the VERBOSE environment variable.

New in version 3.14.

Activates verbose output from CMake and your build tools of choice when you start to actually build your project.

Note that any given value is ignored. It's just checked for existence.

cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=TRUE will generate a file with all compilation commands.

This file is required by some LSP to know how to compile a source file out of the box, but it could also help for debugging compilation problems.

The output file is named ${CMAKE_BINARY_DIR}/compile_commands.json.